Improvements in the specificity of agents used to treat various disease states such as cancer, metabolic, and inflammatory diseases is of considerable interest because of the therapeutic benefits which would be realized if the side effects associated with the administration of these agents could be reduced. Traditionally, dramatic improvements in the treatment of cancer are associated with identification of therapeutic agents acting through novel mechanisms.
Phosphatidylinositol 3-kinase (PI3K or PIK3CA) is composed of an 85 kDa regulatory subunit and a 110 kDa catalytic subunit. The protein encoded by this gene represents the catalytic subunit, which uses ATP to phosphorylate PtdIns, PtdIns4P and PtdIns(4,5)P2. PTEN, a tumor suppressor which inhibits cell growth through multiple mechanisms, can dephosphorylate PIP3, the major product of PIK3CA. PIP3, in turn, is required for translocation of protein kinase B (AKT1, PKB) to the cell membrane, where it is phosphorylated and activated by upstream kinases. The effect of PTEN on cell death is mediated through the PIK3CA/AKT1 pathway.
PI3Kα has been implicated in the control of cytoskeletal reorganization, apoptosis, vesicular trafficking, proliferation and differentiation processes. Increased copy number and expression of PIK3CA or activating mutations in the p110a catalytic subunit of PIK3CA are associated with a number of malignancies such as ovarian cancer (Campbell et al., Cancer Res 2004, 64, 7678-7681; Levine et al., Clin Cancer Res 2005, 11, 2875-2878; Wang et al., Hum Mutat 2005, 25, 322; Lee et al., Gynecol Oncol 2005, 97, 26-34), cervical cancer, breast cancer (Bachman, et al. Cancer Biol Ther 2004, 3, 772-775; Levine, et al., supra; Li et al., Breast Cancer Res Treat 2006, 96, 91-95; Saal et al., Cancer Res 2005, 65, 2554-2559; Samuels and Velculescu, Cell Cycle 2004, 3, 1221-1224), colorectal cancer (Samuels, et al. Science 2004, 304, 554; Velho et al. Eur J Cancer 2005, 41, 1649-1654), endometrial cancer (Oda et al. Cancer Res. 2005, 65, 10669-10673), gastric carcinomas (Byun et al., Int J Cancer 2003, 104, 318-327; Li et al., supra; Velho et al., supra; Lee et al., Oncogene 2005, 24, 1477-1480), hepatocellular carcinoma (Lee et al., id.), small and non-small cell lung cancer (Tang et al., Lung Cancer 2006, 51, 181-191; Massion et al., Am J Respir Crit. Care Med 2004, 170, 1088-1094), thyroid carcinoma (Wu et al., J Clin Endocrinol Metab 2005, 90, 4688-4693), acute myelogenous leukemia (AML) (Sujobert et al., Blood 1997, 106, 1063-1066), chronic myelogenous leukemia (CML) (Hickey and Cotter J Biol Chem 2006, 281, 2441-2450), and glioblastomas (Hartmann et al. Acta Neuropathol (Berl) 2005, 109, 639-642; Samuels et al., supra).
In view of the important role of PI3K-α in biological processes and disease states, inhibitors and/or modulators of this lipid kinase are desirable. In addition, it is well established that combining treatments with different mechanisms of action often leads to enhanced anti-tumor activity as compared to single treatments administered alone. This is true for combinations of chemotherapies (e.g. Kyrgiou M. et. al. J Natl Cancer Inst 2006, 98, 1655) and combinations of antibodies and chemotherapy (e.g. Pasetto L M et. al. Anticancer Res 2006, 26, 3973.
For example, activation of the PI3K pathway contributes to the resistance of human tumor cells to a wide variety of chemotherapeutic agents, including microtubule stabilizing agents such as taxol (Brognard, J., et. al. Cancer Res 2001, 61, 3986-3997; Clark, A. S., et. al. Mol Cancer Ther 2002, 1, 707-717; Kraus, A. C., et. al. Oncogene 2002, 21, 8683-8695; Krystal, G. W., et. al. Mol Cancer Ther 2002, 1, 913-922; and Yuan, Z. Q., et. al. J Biol Chem 2003, 278, 23432-23440). Taxol is widely used to treat advanced cancers including prostate carcinomas, which frequently harbor deletions in the PTEN gene, resulting in elevated signaling downstream of PI3K. A number of preclinical studies suggest that inhibiting signaling downstream of PI3K restores or enhances the ability of chemotherapeutic agents such as taxol to kill tumor cells (Brognard, J., et. al. Cancer Res 2001, 61, 3986-3997; Clark, A. S., et. al. Mol Cancer Ther 2002, 1, 707-717; Kraus, A. C., et. al. Oncogene 2002, 21, 8683-8695; Krystal, G. W., et. al. Mol Cancer Ther 2002, 1, 913-922; and Saga, Y., et. al. Clin Cancer Res 2002, 8, 1248-1252).
Rapamycin, another chemotherapeutic agent, is a potent inhibitor of the mTOR/Raptor complex. Inhibition of mTOR/Raptor prevents p70S6K and S6 phosphorylation, but also leads to relief of a negative feedback loop emanating from p70S6K that serves to downregulate PI3K (Sarbassov, D. D., et. al. Science 2005, 307, 1098-1101). As a result, rapamycin treatment can lead to upregulation of PI3K and increased phosphorylation of AKT (O'Donnell, A., et. al. paper presented at Proc Am Soc Clin Oncol. 2003; and O'Reilly, K. E., et. al. Cancer Res 2006, 66, 1500-1508). Thus, combining rapamycin with inhibitors of PI3K can enhance the efficacy of rapamycin (Powis, G. et. al. Clinical Cancer Research 2006, 12, 2964-2966; Sun, S.-Y., et. al. Cancer Research 2005, 65, 7052-7058).
A growing body of clinical and preclinical data indicates that activation of the PI3K pathway confers resistance to EGFR inhibitors such as erlotinib (Bianco, R., et. al. Oncogene 2003, 22, 2812-2822; Chakravarti, A., et. al. Cancer Res 2002, 62, 200-207; and Janmaat, M. L., et. al. Clin Cancer Res 2003, 9, 2316-2326). Both NSCLC patients with K-Ras mutations and glioblastoma patients with PTEN deletions fail to respond to erlotinib, potentially because of genetic activation of the PI3K pathway (Mellinghoff, I. K., et. al. N. Eng. J Med. 2006, 353, 2012-2024). Preclinical studies have shown that downregulation of PI3K signaling in EGFR-expressing tumor cells confers increased sensitivity to EGFR inhibitors (Ihle, N. T., et. al. Mol Cancer Ther 2005, 4, 1349-1357). Thus, treating cancer with a PI3K inhibitor in combination with an EGFR inhibitor, such as erlotinib, is desirable.
Activation of the PI3K pathway also contributes to the resistance of human tumor cells to DNA damaging agents, such as platins. A number of preclinical studies suggest that inhibiting signaling downstream of PI3K restores or enhances the ability of chemotherapeutic agents such as platins to kill tumor cells (Brognard, J., et. al. Cancer Res 2001, 61, 3986-3997; and Yuan, Z. Q., et. al. J Biol Chem 2003, 278, 23432-23440). Carboplatin is widely used to treat advanced cancers including non-small cell lung carcinomas (NSCLC), which frequently harbor activating mutations in the K-Ras gene, resulting in activation of PI3K (Aviel-Ronen S., et. al. Clin Lung Cancer 2006, 8, 30-38). NSCLC patients with K-Ras mutations do not respond to EGFR inhibitors such as Tarceva, and thus represent a significant unmet medical need (Janne P A, et. al. J Clin Oncology 2005, 23, 3227-3234). Thus, treating NSCLC with a DNA-damaging agent such as a platin in combination with an inhibitor of PI3K is desirable in light of the lack of efficacious treatments.
Treatments that combine an inhibitor of PI3K-α with other anti-cancer agents are desirable and needed.